Abstract
Spectral requirements for the first stage OPO used to pump a tandem ZGP mid-infrared OPO are theoretically investigated. Based on these requirements we demonstrate a singly-resonant type-I OPO including periodically poled KTiOPO(4) and volume-Bragg gratings as output couplers. Singly resonant oscillation is demonstrated very close to degeneracy, where signal and idler spectra are not well separated. Investigations of the longitudinal mode spectrum and the idler spectrum with high resolution using a scanning Fabry-Perot interferometer show the essential role played by the phase correlations of the multi-longitudinal mode Q-switched pump laser in formation of the nonresonant idler spectrum.
Highlights
High average power and high-energy coherent radiation in the mid-infrared (MIR) spectral region spanning wavelengths from 3 μm to about 8 μm is desirable for a number of applications including directed countermeasures, remote sensing and surgery
In the optical parametric oscillator (OPO) with the dielectric mirror output coupler the spectrum extends over 14 THz and, by reference to Fig. 1 it can be seen that most of the generated power would be wasted in the cascaded OPO scheme
For the volume Bragg grating (VBG) output couplers the OPO spectral widths are limited by the monochromator resolution
Summary
High average power and high-energy coherent radiation in the mid-infrared (MIR) spectral region spanning wavelengths from 3 μm to about 8 μm is desirable for a number of applications including directed countermeasures, remote sensing and surgery. One of the methods of obtaining this radiation is by using a tandem optical parametric oscillator (OPO) system which can be pumped by well established Q-switched lasers at 1064 nm. Such tandem OPO consists of a degenerate or near-degenerate OPO operating at 2 μm which in turn pumps a mid-infrared (MIR) OPO employing ZGP or orientation-patterned GaAs [1,2]. In designing the tandem OPO one needs to take into account that the bandwidth of the radiation generated at 2 μm affects the efficiency of the subsequent MIR OPO This is a well known fact, but to answer exactly how much the total efficiency suffers as the 2 μm radiation bandwidth is increased is not straightforward. This is the first question we set to answer in this work
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